I think that the first reason why the root element is HTML based, is
that the idea of an incremental evolution of HTML was born from the
relative failure of xHTML. Now HTML and xHTML have two different
targets. New technologies like the Web Mobile have a native
implementation of xHTML, whereas older browsers doesn't support this
language after several years. It's easier and less onerous to evolve a
render engine step by step than to implement a new language with a lot
of new rules, specifications, etc. So there are more chances that people
move than with a xHTML root element.
--
Deeder, Webdeveloper -- http://www.libert-fr.com/
"Numerical accessibility : more than good manners, it's an attitude"